As a test, I checked the "Require a password reset on next login" box for my account and then logged out.
I tried logging in, expecting some sort of password reset screen, but nothing happened.
I then tried to reset my password at the login screen -- something I was able to do before -- and nothing happened.
In both cases, I get a "500 (Internal Server Error)" in the console.
Any ideas for fixing this? At the very least, can I just reset my password directly in the DB via phpMyAdmin?
FWIW, I also ran into this problem using a Craft demo site.